The intracellular free Ca2+ concentration within cells is low (~1 nM). In muscle

Question

The intracellular free Ca2+ concentration within cells is low (~1 nM). In muscle, a rise in the intracellular Ca2+ concentration causes contraction. Muscle cells then relax when Ca2+ levels are reduced within the cytoplasm. For maximal efficiency, cells rely on two mechanisms to reduce Ca2+ levels: 1) an ATP-driven Ca2+ pump, and 2) an antiporter that exchanges the intracellular Ca2+ for extracellular Na+. Patients with heart disease are often treated with the drug oubain that inhibits the Na+/K+ pump located in the plasma membrane of heart muscle cells. Patient’s hearts beat/contract more strongly following drug treatment, which ameliorates the disease. Provide an explanation for how oubain effects heart muscle contraction and include a diagram to illustrate (8 points). Hint: Keep in mind ion concentration gradients and include all relevant pumps/transporters in your diagram. Your diagram should be simple, like those in lecture 12.

Explanation / Answer

It inhibits action of Na+/Ca+ pumps, so that now Ca2+ is not able to leave the cytoplasm and its concentration is still high. This causes the muscles to stay in contraction state.

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